1. Field of the Invention
This invention relates in general to antenna systems and in particular to antenna systems for wireless information devices.
2. Description of the Related Art
The digital age has brought with it an abundance of options and availability of electronic information. Along with this explosion in electronic information is the availability of portable devices for using this information. For example, electronic books provide users with high quality electronic editions of books, magazines and newspapers. Users download over phone lines thousands of titles from the Internet site of the electronic book providers. As another example, portable web browsers provide users with access to the growing Internet sites to quickly and easily obtain whatever information they require wherever the user is and whenever it is needed usually via conventional telephone lines. The growing market for such portable electronic information devices has led to a growing popularity of wireless information. Wireless information devices allow the user the flexibility of access to the electronic information they desire or require without the additional requirement of telephone landline access.
Wireless information devices such as wireless web browsers and wireless electronic books can be used in multiple physical orientations relative to the user's body. The device can be oriented in the landscape format (short display side vertical), for such activities as web browsing or viewing slides, and then rotated to the portrait format (long display side vertical), for such activities as reading email or reading an electronic book. For maximum reading flexibility, some non-wireless electronic books allow the user to rotate the image in steps of ninety degrees so that, for example, the same side of the device can be held in either hand while reading.
Antenna design creates a challenge for the product designer of wireless information devices used for wireless web browsing or wireless electronic books. Since antenna performance is greatly dependent on the antenna's physical relationship with the body, achieving consistent antenna performance under the conditions surrounding the use of wireless information devices is challenging. No matter where the antenna is placed, depending upon the user's utilization of the product, the antenna can end up under the user's hand, or pressed against the body, resulting in reduced antenna performance.
One conventional approach to this design challenge is the use of antenna diversity. Antenna diversity involves choosing the best signal, or combination of signals, received from multiple antennas. One of the difficulties of this approach in portable products, getting enough space inside the product for the extra antennas, is less of a concern with wireless information devices, due the their relatively large size. However, diversity also requires additional power for the duplicate receiver signal paths required, and this can significantly affect product battery life. The addition of a duplicate receiver can also increase manufacturing cost of the device. There is also additional signal quality estimation that must be performed on the signal from each antenna. Lastly, a scheme for the choice of the proper transmit antenna is required. For these reasons, antenna diversity is not an optimum solution to this problem.
Alternatively, the product designer can either accept a reduction in wireless performance for some orientations of the wireless information device, or eliminate the ability for users to orient the wireless information device in the multiple orientations providing the most ergonomically pleasing orientation for each of a multiplicity of functions. Both of these options can reduce the utility and/or desirability of the wireless information device.
What is needed is an antenna system that allows the user to orient the wireless information device relative to the user's body in a multiplicity of orientations with consistent product performance without additional cost or size to the product.